Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $38.48   6.384%   $40.9366   $40.94   $40.95   $40.90  
  Purchase #2 $242.33   11.160%   $269.374   $269.37   $269.35   $269.40  
  Purchase #3 $224.86   7.207%   $241.0657   $241.07   $241.05   $241.10  
  Purchase #4 $152.47   9.132%   $166.3936   $166.39   $166.40   $166.40  
  Purchase #5 $71.33   12.865%   $80.5066   $80.51   $80.50   $80.50  
  Purchase #6 $175.45   11.122%   $194.9635   $194.96   $194.95   $195.00  
  Purchase #7 $29.88   13.860%   $34.0214   $34.02   $34.00   $34.00  
  7 purchase totals = $934.80       $1,027.2614   $1,027.26   $1,027.20   $1,027.30